Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data services. The wireless communication system is generally a multiple access system that can support communication with multiple users by sharing available radio resources (e.g., bandwidth, transmit power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for supporting broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. In the IEEE 802.16a standard approved in 2003, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ were further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 was completed in 2005 in a format of ‘corrigendum’. A standard based on the IEEE 802.16-2004/Cor1 is referred to IEEE 802.16e or WiMAX.
In the IEEE 802.16 broadband wireless access working group, there is ongoing standardization effort for the IEEE 802.16m standard which is a new technical standard based on the IEEE 802.16e. The IEEE 802.16m standard requires flexible support for the conventional IEEE 802.16e standard as well as a new system.
In the IEEE 802.16e standard, in general, data is mapped to physical subcarriers in a physical layer according to two steps. In a first step, the data is mapped to at least one data slot on at least one logical subchannel. In a second step, each logical subchannel is mapped to a physical subcarrier. This is called permutation. Examples of a permutation rule introduced in the IEEE 802.16e standard include full usage of subchannels (FUSC), partial usage of subchannels (PUSC), optional-FUSC (O-FUSC), optional-PUSC (O-PUSC), adaptive modulation and coding (AMC), etc. A set of OFDM symbols using the same permutation rule is referred to as a permutation zone.
FIG. 1 shows a frame structure of the conventional IEEE 802.16 system. This may be found in the section 8.4.4.2 of the IEEE 802.16-2004 standard. An OFDMA frame includes a downlink (DL) frame and an uplink (UL) frame which are time-division duplexed. The DL frame temporally precedes the UL frame. The DL frame consists of a preamble and a plurality of permutation zones. The UL frame consists of a plurality of permutation zones.
In the conventional frame structure, the permutation zones are divided in a time domain. In addition, in the same time domain, the same permutation rule is applied to a full frequency domain. A base station (BS) can switch the permutation zones according to a channel condition reported from a user equipment (UE).
The above frame structure has the following problems.
First, since the same permutation rule has to be applied in one or a plurality of OFDM symbols, flexibility for resource allocation is not sufficient. In general, both users having high channel selectivity and users having high frequency diversity gain co-exist in a cell for a specific time period. It is preferable that the users having the high channel selectivity use the AMC. In addition, it is preferable that the users having the high frequency diversity gain use the FUSC. Therefore, the resource allocation flexibility is not sufficient to satisfy users having various channel conditions in the same time period.
Second, since resources are allocated in a subcarrier unit when using a permutation rule such as the FUSC, it is difficult to apply a space frequency block code (SFBC) scheme in which a plurality of subcarriers have to be grouped in pair.
Third, although the conventional structure is designed to minimize inter-cell interference when the same permutation zone is used at the same time point between cells, a probability that the same permutation zone is used at the same time point between the cells is actually not much high after a first permutation zone. Therefore, it is difficult to properly utilize advantages of the structure designed to minimize inter-cell interference between permutation zones.